The Schematic Design And FEA Of Fabricated Piers With External Prestressing

In our country, the backward construction technology and long period construction have been resulted in city's traffic congestion and environmental pollution.These problems have been restricted the economic and social development.To accelerate the urban bridge construction, it should be easy traffic congestion and reduce envrionmental pollution, a schematic of prefabricated bridge piers with external prestressing was presented in this paper. The advantage of these piers can be ability to produced in factories, assemble on site, and be conductive to bridge monitoring, maintenance and easly removable. The prefabricated units can also be recycled in order to meet emission reduction requirements, and the external prestressing strand can be removed, replaced and re-tensioned.The main idea of this paper is as follows:Firstly prefabricated bridge piers with external prestressing were designed, and then precast cap beam, precast pier and pier cap were calculated respectively. In the construction used phase by phase to attained the designed.Secondly, ANSYS finite element analysis software was used to calculate with control sections of these piers respectively in the construction phase by phase, which include three loading conditions.Finally, in the ANSYS finite element software, the earthquake response spectrum was used to simply analysis seismic performance of these piers.ANSYS finite element analysis result, the main conclusions are as follows:(1) The maximum displacement of the pier occurs at the top of pier; the maximum vertical displacement occurs in the first loading condition, its value is 1.68mm; the maximum horizontal displacement along the bridge occurs in the second loading condition, and value is 0.61mm; the maximum transverse displacement occurs in the third loading condition, and its value is 1.65mm.(2) Under the role of prestress and three loading conditions, the pier stress is-1.55MPa～-18.3MPa, which does not exceed the design value of compressive strength of concrete.The conclusion shows that the design of bridge piers is reasonably practicable and its strand stress range is 981MPa～997MPa, which does not exceed the design value of tensile strength and compared with the effective prestress, the loss of prestress steel strand is smaller. (3) In the use phase of the bridge, the maximum tensile stress of the concrete at the end of steel strand is 6.34MPa, which is more than the design value of concrete strength.Therefore, the strengthening treatment should be carried out in the design of piers, for example,the steel plate with the size's 210mm×210mm×30mm and 4 layer spiral reinforcement are set in the anchor end and jacking end.(4) In the longitudinal effect of the earthquake, when using tensile stressσcon=0.65fptk andσcon=0 respectively, the former top pier displacement along the bridge is 15.25% the latter one. The former pier earthquake function is 1.38 times the latter pier. In the transverse effect of the earthquake, the former top pier displacement along the bridge is 3.26% of the latter's; and the former's earthquake function is the 0.97 times latter's. In conclusion the prestress structure is more sronger than not prestressed one.(5) In the longitudinal effect of the earthquake, the maximum tensile stress occurs at the end of piers, its value is 0.52 MPa and less than the design strength.When the precast bridge piers are used in high seismic fortification intensity region, the shearing force in the bottom of piers is beyond the shear capacity, therefore, the precast bridge piers are not suitable for this region.